1. Field of the Invention
This invention relates generally to mobile drill rigs for advancing drill rods into the ground and retracting drill rods from the ground. In particular, the present invention relates to devices and methods for retracting a drill rod from the ground using a hydraulic clamp assembly carried on the drill head.
2. Description of the Related Art
A mobile drill rig can be used for many tasks, including: soil core and soil gas sampling, groundwater sampling and testing, geotechnical investigation, installing geothermal ground loops, contaminant logging, grouting, and materials injection. A typical drill rig includes a power unit, a drill mast, positioning features (e.g., movement fore and aft, tilt of the drill mast, outriggers, and so forth), drill head, and support hardware (e.g., pumps, winch, and so forth).
There are two conventional techniques for advancing tooling into the ground: drilling and direct push. When drilling, the subsurface material is brought to the surface. Typical drilling techniques are: augering, coring (e.g., core drill, sonic drilling), and cut and flush (e.g., air/mud rotary and down hole hammer). Instead of removing material, a direct push technique uses the static weight of the drill rig and, typically, a hydraulic hammer to displace the excess material into the surrounding formation.
Advancing the drill rod into the ground is only the first part of the procedure; the drill rod must be retracted from the ground as well. Historically, an operator was limited to the following methods of retracting the drill rod:
1. Thread onto the drill rod with the head spindle and use the head to pull back the drill rod. This method had the negative effects of wear on the threaded components and blocking access to the inner diameter of the rod while pulling.
2. Thread on a pull bail and use an overhead winch. This method had the negative effects of safety concerns and typically pulling over the drill rod centerline, making it difficult to access the inner diameter of the drill rod.
3. Upset top cap. This method had the negative effects of requiring threading on a cap, and typically blocking access to the inner diameter of the rod while pulling.
4. Upset on drill rod. This method had the negative effect of requiring the drill rod to be engaged and pulled only at specific height intervals.
5. Manual drill rod grip pull system. This method had the negative effect of a non-positive grip and being difficult to use with long drill rod lengths.
6. Casing jack. This method had the negative effect of being slow and typically having a limited stroke length.
There is a need in the industry for an improved device and technique for retracting drill rod strings from the ground.